The muscles of the human body tend to get tired when one is sitting in an uncomfortable position or in the same position for long periods of time. Humans sit most while working and discomfort is most noticeable during tasks requiring creativity or concentration. For this reason commercial and home office furniture usually includes multiple points of adjustment. Additionally, such furniture may have cushioning so as to lessen the reciprocal pressure that a supporting surface of a chair exerts on a sitter's body. Such chairs are generally able to rise and sink, lean back and swivel. Some, especially the more costly examples have adjustable armrests, lumbar supports, massagers and extra layers of cushioning.